With the remarkable development of small, thin, and high-functionality portable electronic devices of the recent years, there is a growing demand for small, thin, and high-capacity batteries as the power source of these devices. Generally, lithium batteries can be structured small with a high capacity. In particular, flat prismatic lithium ion rechargeable batteries are suitable for the devices to be made thinner, and therefore they have been increasingly used as the rechargeable battery for portable electronic devices such as mobile phones.
There is known a battery pack used as a power source of various devices, including a battery and a circuit substrate provided with an overcurrent limiting means, a protection circuit against overcharge/overdischarge, and external connection terminals. The battery and the circuit substrate are placed in predetermined positions in an outer case having windows for exposing the external connection terminals, and configured as a battery pack. The circuit substrate is connected to connection terminals of the battery with leads (see, for example, Japanese Patent Laid-Open Publication No. 2002-231201).
There is also known a battery pack wherein a terminal substrate provided only with external connection terminals is used instead of the circuit substrate (see, for example, Japanese Patent Laid-Open Publication No. 6-333547).
Electronic devices are generally formed with a battery pack accommodating space in which the battery pack can snugly fit, and has a connection terminal that makes resilient contact with the external connection terminals on the same surface of the battery pack when the battery pack is accommodated for electrical connection therewith.
One example of the configuration of such a battery pack in which a circuit substrate or terminal substrate having external connection terminals is retained in the outer case is described with reference to FIG. 7A and FIG. 7B. Reference numeral 51 denotes a flat prismatic battery pack comprising a battery 32 structured as a lithium ion rechargeable battery and a circuit substrate 33 or a terminal substrate accommodated in an outer case 34 that is divided in two in a thickness direction. The circuit substrate 33 is connected to connection terminals 35a and 35b of the battery 32 with leads 36.
The battery 32 is formed of elements for electromotive force 38 encased in a battery case 37 having an open end sealed with a sealing member 39, which is formed with a protruding connection terminal 35a of one polarity, with an insulating gasket 40 interposed therebetween. The battery case 37 serves as the connection terminal 35b of the other polarity. The outer case 34 has windows 42 in one end wall 41 for exposing the external connection terminals provided on the circuit substrate 33, and an engaging projection 44 for holding the circuit substrate 33 such as to make contact with the inner surface of the end wall 41.
When the battery pack 51 shown in FIG. 7A and FIG. 7B is inserted in the battery pack accommodating space of a portable electronic device, a connection terminal makes contact with the external connection terminals with appropriate resiliency to establish electrical connection. However, since the circuit substrate 33 or terminal substrate provided with the external connection terminals is arranged such as to make contact with the end wall 41 of the outer case 34, the position of the external connection terminals varies depending on errors in the height H of the outer case 34. As the outer case 34 is a resin molded component and has a large height H, the errors tend to be large. Accordingly, there is a problem that sufficient reliability is hard to achieve in terms of the contact state between the external connection terminals of the battery pack 51 and the connection terminal in the battery pack accommodating space.
A possible solution for controlling the errors in the height of the battery pack within a predetermined range is to form the battery 32 and other components integrally by mold forming. However, the mold forming has several drawbacks such as poor productivity, high facility cost, and a potential large profit loss due to defective products resulting from possible molding troubles.
In view of the problems in the conventional technique described above, it is an object of the present invention to provide a battery pack that is highly reliable in respect of the contact state of its external connection terminals when set in a portable electronic device, a battery pack that has a simple and low-cost configuration and yet minimizes battery damage due to drop impact, and a manufacturing method of this battery pack.